1. Field of the Invention:
The present invention relates to a multicarrier receiver and a transmitter with a delay correcting function, and particularly to a multicarrier receiver which suppresses a deviation in delay time for each carrier at a receiving section upon dealing with a multicarrier, and a transmitter with a delay correcting function which corrects a delay between transmission and feedback for a distortion analysis.
2. Description of the Related Art:
FIG. 15 is a configuration diagram showing one example of a conventional multicarrier receiver.
In the same drawing, reference numeral 101 indicates a DUPlexer (DUP) which has a filter whose one end is connected to an antenna (not shown) capable of transmitting and receiving a multicarrier and which separates a transmit signal to the antenna and a receive signal from the antenna, using the difference between frequencies for transmission and reception.
Reference numeral 102 indicates a low noise amplifier which amplifies a receive signal to a desired level.
Reference numeral 103 indicates a BPF (Band Pass Filter) which extracts only a band necessary for reception.
Reference numerals 104 through 108 correspond to each of receivers, which is used for a given specific carrier frequency. It is hereinafter called “single carrier receiver 109”. The single carrier receivers 109 are provided by the number of carriers to be received, and the output of the BPF 103 is distributed and inputted thereto.
Reference numeral 104 indicates a mixer which performs frequency conversion from a radio frequency band to an intermediate frequency allowed to pass by a narrow-band BPF 105.
Reference numeral 105 indicates the narrow-band BPF. In the present example, a SAW (Surface Acoustic Wave) filter is assumed to be used as the narrow-band BPF. It is common that the SAW filters are constructed in two stages in cascade form to obtain attenuation in terms of application to radio equipment. Therefore, a two-stage configuration is adopted.
Reference numeral 106 indicates an A/D converter which converts an analog signal to a digital signal.
Reference numeral 107 indicates a quadrature detector, which digitally quadrature-detects an intermediate frequency signal to a baseband I/Q signal.
Reference numeral 108 indicates an LPF which deletes a double frequency component generated at the quadrature detector 107 and performs a band restriction.
As another related art associated with the present invention, there is known one wherein a fractional delay filter for realizing a slight delay is applied to wireless communication equipment (refer to, for example, a patent document 1 (Japanese Patent Laid-Open No. 2001/217892)).
FIG. 16 is a block diagram showing a configuration of a transmitter of a conventional base station apparatus employed in a mobile communication system such as a W-CDMA (Wideband-Code Division Multiple Access) system or the like.
In the same drawing, each input baseband signal is supplied to a digital modulator 1001, where processes such as band restrictions made every I and Q phases of the baseband signal, upcoversion to an IF (Intermediate Frequency) and digital quadrature modulation are carried out. A D/A (Digital/Analog) converter 1002 converts the baseband signal into analog I and Q phases. These I and Q phases are supplied to a frequency converter 1003 where they are quadrature-modulated and upconverted into an RF (Radio Frequency) signal. A signal outputted from the frequency converter 1003 is power-amplified by a power amplifier 1004, which in turn is transmitted from an unillustrated antenna.
FIG. 17 is a configuration diagram showing one example of the digital modulator 1001 shown in FIG. 16.
Let's assume that I components of N (where N: integer greater than or equal to 2) baseband signals are inputted to the digital modulator 1001 in the same figure. In this case, the digital modulator 1001 is provided with N band restriction filters 1001a, 1001b, . . . , 1001c, N upfilters 101d, 1001e, . . . , 1001f, and N digital quadrature modulation sections 1001g, 1001h, . . . , 1001i. A frequency band for an I component of a baseband signal f1 is restricted to a predetermined form at the band restriction filter 1001a. A sampling frequency (sample rate) is upconverted by the upfilter 1001d and digitally quadrature-modulated by the digital quadrature modulation section 1001g, whereby a quadrature-modulated IF signal is obtained in which the sample rate is 92.16 MHz, for example. Similarly, frequency bands for respective I components of baseband signals f2, . . . , fN are also restricted to predetermined forms at the band restriction filters 1001b, . . . , 1001c respectively. Sampling frequencies (sample rates) are upconverted by the upfilters 1001e, . . . , 1001f and digitally quadrature-modulated by the digital quadrature modulation sections 1001h, . . . , 1001i respectively, whereby quadrature-modulated IF digital signals are obtained in which the sample rates are 92.16 MHz, for example.
The thus-obtained quadrature-modulated IF digital signals of N I components are added together by an adder 1001j. Consequently, an IF signal is obtained in which the I components of the respective baseband signals f1 to fN are combined together by quadrature modulation. The IF composite signal of I components is supplied to the D/A converter 1002 shown in FIG. 16.
Similarly, Q components of the baseband signals f1 to fN are also subjected to similar processing, so that an IF composite signal of Q components in which the Q components are combined together by quadrature modulation, is obtained from the digital modulator 1001, after which it is supplied to the D/A converter 1002 shown in FIG. 16.
In FIG. 16, the IF composite signal of I components and the IF composite signal of Q components both outputted from the digital modulator 1001 are respectively converted to analog IF composite signals by the D/A converter 1002. The IF composite signal of I components and the IF composite signal of Q components are combined together by quadrature modulation at the frequency converter 1003 to result in an RF signal for one channel.
Realizing one multicarrier receiver by unifying the plurality of single carrier receivers 109 as described above mainly results from the restrictions of the dynamic range and sampling frequency of the A/D converter 106. This is of an extremely general receiver configuration. There has heretofore been no problem under such a configuration. However, it has recently been found out that a deviation in delay time presents a problem upon the process of bringing into multicarrier form, that is, the process of consolidating plural carriers subjected to reception processing into one again and transmitting the same to a baseband signal processor through an interface between the receiving section and the baseband signal processor (block located in a stage subsequent to the single carrier receiver 109).
In a receiver that performs a multicarrier communication as in a multicarrier mode in a CDMA 2000 system, a baseband signal processor normally operates with the times required to propagate respective carriers as being equal to each other. That is, it does not grasp a deviation in delay time for each carrier. Assuming that this presumption is not made and the deviation in delay time varies, the baseband signal processor must always grasp, by use of a DLL or the like, the deviation in delay time between the carriers at an arbitrary channel at which the multicarrier communication is being performed, and perform such complex processing as to correct the deviation in delay time for each carrier. Even upon execution of such processing, the interface to the baseband signal processor is normally implemented at a sampling frequency which is as slow in speed as possible, for the purpose of reductions in cost and size. Time resolution is not sufficient at the reduced sampling frequency. Since the sampling frequency is returned to a high sampling frequency by complex signal processing (interpolation or the like) and thereafter correction is made, the configuration of the interface is made inefficient. Therefore, the deviation in delay time on the multicarrier receiver side is prescribed so as to fall within a predetermined range.
In general, however, analog parts always have delay deviations due to individual variations in parts and a change in temperature. In particular, the filter parts like the DUP 101, BPF 103 and narrow-band BPF 105 are large in delay and increase in deviation too. Deviations in delay time of devices employed in the CDMA 2000 receiver will be explained by way of example. In the DUP 101, its deviation results in ±50 nsec, and in the SAW filters of the narrow-band BPF 105, their deviations result in +60 nsec/−50 nsec (upon two-stage configuration) respectively. The worst supposed delay deviation results in +110 nsec/−100 nsec. There is a possibility that this will exceed a prescribed value (±102 nsec @cdma2000) of the interface global standard for a transmission amplifying device with a transmitting/receiving function, which is referred to as “CPRI (Common Public Radio Interface)”.
Thus, the related art has adapted to the reduction in delay deviation produced for each carrier by increasing each analog constituent part in cost and size in order to reduce the delay deviation. When an attempt is made to greatly ensure the amount of out-of-band attenuation in the neighborhood of a desired band in each SAW filter, for example, a delay deviation increases too. Therefore, an attempt has been made to relax the amount of out-of-band attenuation per SAW filter and instead increase the number of multistage connections. In the present method, however, the gain is lost by about 10 dB each time the number of SAW filter stages increases by 1, so that amplifiers are also additionally provided. Thus, solid variations in all these parts, their changes in temperature, etc. must be managed, and adaptation to mass-production becomes difficult due to an increase in the number of parts.